The inflammatory reaction following coronary vessel occlusion is toxic for the myocardium. Endothelial cells, downstream from an acute occlusion, play a pivotal role in this response and are responsible for anchoring, through specific adhesive molecules, circulating leukocytes which mediate the cellular inflammatory reaction. The endothelial cells then fail to provide their function as structural support and as signal transduction interface for the vessel wall and the surrounding myocardium. While cytokines and free radicals are known mediators of the endothelial cell collapse, the signalling mechanisms within endothelial cells regulating endothelial cell changes remain unknown. This project aims at investigating the role of the tyrosine kinase pathway as a key signalling system controlling endothelial cells undergoing hypoxia and reoxygenation. Our preliminary results indicate that as a result of hypoxia, the tyrosine kinase signalling pathway of endothelial cells is activated and in particular at the level of focal adhesions. Concurrently, the actin cytoskeleton s reorganized with most of the actin filaments concentrating at the periphery of the cells. Such changes are usually observed in cells activated by growth factor receptors which have a tyrosine kinase on their cytoplasmic domain. Therefore, we propose to develop the following specific aims: (1) Determine the effect of hypoxia and reoxygenation on tyrosine phosphorylation and translocation of known tyrosine kinase substrates, including phospholipase Cgamma1, phosphatidylinositol 3-Kinase, Src homology containing protein Src which connects receptor tyrosine kinase and Ras, and focal adhesion tyrosine kinase pp125FAK, and quantify the changes in filamentous actin superstructure in hypoxic and post-hypoxic cells; (2) Characterize the role of pp125FAK in the mechanism leading to endothelial cell-leukocyte interaction under conditions of normoxia, hypoxia, and reoxygenation; (3) Study the effect of the major actin regulating growth factor for endothelial cells, hepatocyte growth factor/scatter factor on the motility and cytoskeletal organization of endothelial cells in normoxic, hypoxic and post-hypoxic conditions; (4) Assess the ability of tyrosine kinase inhibitors to reduce infarct size in a rat model of coronary occlusion/reperfusion and characterize the consequences of tyrosine kinase inhibition on left ventricular remodeling. These experiments will greatly improve our understanding of the mechanisms leading to endothelial cell dysfunction and myocardial inflammation induced by coronary occlusion and reperfusion, thereby allowing us to develop new strategies to reduce myocardial damage induced by infarction.